Multicasting is a network technology for delivering information to a group of recipients simultaneously. Multicasting can be referred to as point-to-multipoint data transmission as well.
Multicast services are becoming more and more popular with the development of cellular wireless networks. For example in LTE (Long Term Evolution) networks data can be transmitted to multiple recipients by eNB (evolved Node B). By utilizing the shared nature of wireless medium, multicast service can be realized with a high efficiency.
HARQ (hybrid ARQ, Automatic Repeat reQuest) protocol can be incorporated into the packet multicasting process in order to support reliable packet delivery in a multicast service. In that case, each user in the group of recipients will feedback an ACK/NACK message for the multicast packets, and a packet will be retransmitted, if a NACK message for it is reported by one of the members of the group of recipients.
US2006/0291410 discloses a solution for multicast retransmissions. If one recipient sends a negative acknowledgement, the other recipients are informed that it is no longer necessary to provide feedback, since retransmission will be initiated anyway.
Also a scenario in which members of a group of recipients of a multicast transmission take care of the retransmissions has been proposed. That is, a recipient that successfully received a packet retransmits the packet to recipients that didn't receive the packet or received it with errors. For example “Cellular controlled short-range communication for cooperative P2P networking,” F. H. P. Fitzek, M. Katz, and Q. Zhang, Proc. Wireless World Research Forum, Heidelberg, 2006 discloses one such solution.